Selective adsorption can separate a desired component from a feed mixture by adsorbing the desired component while letting other components in the mixture flow by. The other components are referred to herein as “undesired components” to differentiate them from the desired component, but the undesired components may be used for other purposes or processes and therefore be desirable in their own right. An adsorption separator may use an adsorbent that has a higher affinity for the desired component than for the undesired components in the mixture, so the desired component is adsorbed on the surface and within pores, cavities, or other areas of the adsorbent. The adsorbent may adsorb some of the desired component, the undesired components, and other compounds, but the more preferred compounds are adsorbed more readily. Selective adsorption can also proceed by adsorbing undesired components and allowing the desired component to flow through the adsorbent for collection. In this description, the desired component is adsorbed by the adsorbent, but this description is also applicable to embodiments where the undesired components are adsorbed and the desired component flows through the adsorbent.
As the mixture flows over the adsorbent, the desired component is adsorbed so the fluid passing through the adsorbent has a lower concentration of the desired component, and therefore a higher concentration of other components. This adsorption process diminishes after a period of time because the available adsorption sites on the adsorbent are taken up. The undesired components in the mixture may then be drained or displaced from the adsorbent in a purification process. Additional fluid flowing through the adsorption bed pushes the undesired components out. A desorbent may then be introduced into the adsorbent bed, where the adsorbent preferentially adsorbs the desorbent over the desired component. The desorbent displaces the desired component from the adsorbent in a desorption process, and the desired component can then be collected with some excess desorbent.
A moving bed adsorption separator uses a plurality of adsorption beds filled with adsorbent, and the adsorption beds are passed through different “zones” for different process steps. For example, a first zone may introduce the mixed feed to the adsorption bed to remove the desired component, and a second zone may be a purification zone where the undesired components are removed in a raffinate. A desorption zone may follow the purification zone, where the desired component is desorbed and recovered. In a simulated moving bed separator using an adsorbent, a plurality of adsorption beds are fluidly connected together and fixed in position. Some simulated moving bed separators use a plurality of adsorption beds fluidly coupled in a circular manner, so fluids flow through the adsorption beds in a loop. i.e., fluid flows from the first adsorption bed into the second adsorption bed, fluid flows from the second adsorption bed into the third adsorption bed, and so on, and fluid from the last adsorption bed flows into the first adsorption bed. The adsorption beds pass through the various zones by changing or shifting feed and take-off locations from one adsorption bed to the next, where the relative position of the feed and take-off locations determine the zone each adsorption bed is in. For example, a plurality of conduits fluidly couple the adsorption beds to a distributor, and the distributor shifts or changes the feed bed, or the adsorption bed where the feed stream is introduced to the adsorption beds. The distributor changes the feed bed from one adsorption bed to an adjacent adsorption bed, and also changes other feeds and extractions from the adsorption beds. After a period of time, the distributor changes the feed bed again, such that each adsorption bed serves as the feed bed in turn.
The desired component is removed from the simulated moving bed separator in an extract, where the desorbent is fed into the adsorption beds to displace the desired component, as described above. The extract includes the desired component and the desorbent, which can be separated by distillation. The distributor changes the conduit used to remove the extract, and that conduit is rinsed before use to increase the purity of the recovered product. The conduit is typically rinsed with the desorbent because the desorbent will be present in the extract and the distillation system is in place to separate the desorbent from the desired component. However, energy is required to separate the desorbent and the desired component by distillation. The higher the concentration of desorbent, the more energy that is needed for the distillation.
Accordingly, it is desirable to develop methods and apparatus to separate a desired component from a mixture with a simulated moving bed separator that produces an extract with a higher concentration of desired product than when the extract conduit is rinsed with a desorbent. In addition, it is desirable to reduce the total amount of energy needed to recover the desired product than when the extract conduit is rinsed with a desorbent. Furthermore, other desirable features and characteristics of the present embodiment will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.